This invention relates to a process for the preparation of 9-tricosene and 9-heneicosene, the cis-isomers of which are essential components of the sex pheromone of the housefly Musca domestica.
As is known, pheromones are substances which serve in general to stimulate chemically mediated behavioral interactions of organisms with one another, in a narrower sense such interactions of insects with one another. Thus, among the pheromones are counted primarily sex attractants, as well as substances causing the expression of alarm, aggregation, attack, defense, etc., of the insects; these pheromones are generally effective even in minute quantities. By the use of refined analysis and synthesis methods, numerous pheromones have been isolated in recent years, explained with regard to their constitution and in part even synthesized. Among these pheromones is cis-9-tricosene, the sex attractant of the housefly, which is also known under the name of muscalure; see D. A. Carlson et al, Science 174:76-78 (1971). It has been discovered that, in addition to cis-9-tricosene, several other cis-olefins with a double bond in the 9-position are effective as sex pheromones; in particular, a mixture of cis-9-tricosene and cis-9-heneicosene in a weight ratio of 7:3 is said to possess optimum effectiveness, as has been reported by A. Mansingh et al, Can. Entomol. 104:1963-65 (1972).
The sex pheromones are of considerable practical interest inasmuch as it is possible with their aid to selectively combat individual, damaging types of insects. The procedure followed is to attract individual insects of the type to be combated with the aid of the sex pheromone and then to destroy the insects by means of insecticides or electric traps and/or to prevent the insects from reproducing by chemosterilization or radiosterilization. In this way, the populations of destructive types of insects can be reduced to a tolerable level without the danger of exerting an adverse effect on harmless or useful types of insects.
The common housefly Musca domestica is generally counted among the destructive insects, since it can transmit numerous diseases and deposits eggs in foodstuffs which are rendered unfit for consumption due to the evolving maggots.
The most effective component of the sex pheromone of the housefly, cis-9-tricosene, was isolated, characterized and synthesized for the first time by D. A. Carlson et al by means of a Wittig synthesis from 1-nonanal and 1-bromotetradecane; see Science 174: 76 - 78 (1971).
Further syntheses of cis-9-tricosene which have become known in the meantime are:
The alkylation of pentadecinyllithium with n-octyl bromide and the subsequent partial hydrogenation of 9-tricosine reported by K. Eiter in Naturwiss. (Natural Sciences) 59:468 (1972);
Reaction of erucic acid with 2 moles of methyllithium and subsequent Huang-Minlon reduction of the ketone by R. L. Cargill and M. G. Rosenblum, J. Org. Chem. 57:3971 (1972);
Reaction of oleic acid with 2 moles of n-pentyllithium and/or of oleonitrile and n-pentylmagnesium bromide and subsequent Huang-Minlon reduction reported by T. L. Ho and C. M. Wong in Can. J. Chem. 52:1923 (1974);
Combined electrolysis (crossed Kolbe synthesis) of the sodium salts of oleic acid and enanthic acid in a methanolic sodium methylate solution by G. W. Gribble et al, reported in Chem. Comm. 735 (1973); and
The Wittig synthesis from 1-nonanal and tetradecyl bromide by H. J. Bestmann et al, "Chemiker-Ztg." (Chemists' Periodical) 98:161 (1974).
None of these multistage syntheses offers the possibility of producing the sex pheromone inexpensively on a large commercial scale, since they are all inherently based on stoichiometric reactions of natural substances or derivatives thereof with expensive auxiliarly chemicals and form economically worthless by-products.